Various methods and apparatus have been used to efficiently pump lasers and to get the maximum output from the laser pumping medias. For example, U.S. Pat. No. 3,311,844 (DiCurcio) disclosed a "high-speed" pulsed laser system. It uses multiple rods that are secured to the periphery of a wheel. The rods are rotated into a laser cavity and pulsed pumped and fired. However, "high-speed" for this system is 1 Hz with very high power. Also embodied in this patent is cooling of the rods by a method of selective indexing. This system also shows that multiple pumping lamps can be used to pulse pump these one or more rods in the pumping chamber. These lamps are flashed in coordination with the passage of the rods through the pumping chamber to deliver pumping energy to the rod in the chamber. In this manner the lamps are fired sequentially to avoid excessive heat build-up in any one lamp. If it is desired to cool each laser rod after the rod has been pulsed, one or more cooling devices such as fans or blowers can be placed around the periphery of the system to deliver a flow of cooling air to cool the laser rods after they have been pulsed.
U.S. Pat. No. 4,555,786 (Byer) discloses another high power solid state laser. It describes a laser system where the motion of the laser medium is solely for the purpose of thermal load distribution. Reference is made to a spinning glass disk or slab. The purpose of moving the lasing medium is to reduce thermal stress in the glass disk or slab to keep it from breaking. This patent also shows that the lasing slab or disk can be cooled by using a film of an index matching fluid. This film is applied on the surface of the rotating lasing disk to transfer the heat from the rotating disk or slab to a cooling sheet or plate.
U.S. Pat. No. 4,567,597 (Mandella) discloses a laser system having a stationary lasing region. The lasing medium is rotated to bring thermally cooled unpumped portions into the lasing cavity and where it is pumped and then allowed to lase, and the lasing media is then rotated out of the lasing cavity so that heat is transferred out of the cylinder to the surroundings. This patent also discloses a laser rod in the shape of a hollow cylinder that is rotated so that the cooled and non-excited region is brought into the resonator cavity, is allowed to lase, the then fired portion of the hollow laser rod is rotated out so that heat is transferred out of the hollow cylinder to the surroundings.
U.S. Pat. No. 4,575,854 (Martin) discloses another unique pumping scheme for Nd:YAG lasers. Instead of using an arc lamp, a bank of laser diode arrays or an array of laser diodes surrounds the cylindrical rod. These laser diode arrays are sequentially pulsed to provide CW pumping, by insuring that at least one diode array is on while the others are off. Each diode array actually operates at quite a low duty-cycle for cooling purposes. The stationary Nd:YAG laser rod is pumped by the surrounding array of diode laser bars, which are electronically fired in rotation.
U.S. Pat. No. 4,845,721 (Hoffmann) discloses a solid state laser rod having internal bores through which a coolant can flow. Hoffmann also discloses rotating the rod so that only specific portions of the laser materials are subjected to pumping while other portions are cooling. This patent also describes means by which solid-state laser media can be cooled through special designs/shapes of the actual material. These designs facilitate laser cooling by increasing surface area for heat extraction. Reference is made to a tubular shaped rod (empty cylinder) which is rotated into the resonator pumping region, however, this is done solely for cooling purposes.
U.S. Pat. No. 4,890,289 (Basu et al.) discloses a rotating disk laser which is optically pumped by a source positioned off center from the axis of rotation of the lasing disk. This patent describes both rotation or translation of the lasing medium for the purpose of thermal load distribution. Reducing the thermal effects caused by lamp pumping is the main purpose of this patent. It incorporates diode-pumping with delivery of that radiation via fiber optics Additionally, the rotation of the medium is solely for the purpose of reducing thermal stress in the medium.
This invention, however, discloses a solid state lasing rod that is spun at high rates of speed on its long axis The rod is of a size, larger than the size of the aperture through which the lasing beam passes. While the rod is spun, within a mirrored cavity, the rod is pumped with photons Because the laser rod is larger than the aperture, the laser beam to be used for processing can be off-centered from the rod axis. The beam of light through this off-axis aperture is then amplified by the rod and transmitted through the end mirrors and then is directed to the work-piece.
The spinning rod increases the laser repetition rate, because as the rod spins, the area of the rod that is not releasing photons or not lasing is being charged or pumped with photons, so that each area that lases is fully charged when it is rotated to lase through the aperture.
A hollow solid state lasing rod can also be used with this invention. In such a case, the hollow lasing rod is pumped with photons from inside, and/or outside. The hollow rod can be spun using off-axis apertures and still get results which are similar to the ones obtained using a solid state lasing rod.
The hollow lasing rod could also be cooled from the inside using water or other fluids. Other liquids or gas medium, e.g. liquid nitrogen or freon, can also be used to cool the hollow or the solid state lasing rod from the outside.
This invention also discloses that fluid or water bearings can be used when either the solid or hollow solid state laser rod is being spun. In such a case, the fluid is not only used to cool the bearing surfaces of the solid state laser rod but also acts as a lubricant.